Polyurethanes have been used for a long time in numerous fields of application for highly diverse purposes. Depending on the choice of starting materials and the stoichiometric ratio of the starting materials, polyurethanes are obtained with very different physicochemical properties.
Thickeners are used widely for increasing the viscosity of aqueous preparations, for example in the fields of cosmetics, human and animal nutrition, pharmacy and for detergents, paints and coatings. Inter alia, polyurethanes are also known as thickeners.
For example, polyurethane solutions or dispersions in water-dilutable aqueous or predominantly aqueous phase are referred to by the person skilled in the art as HEUR thickeners (“hydrophobically modified ethylene oxide urethane copolymer”), and have already been used for a relatively long time in highly diverse fields of application, for example for thickening water-based emulsion paints.
The action principle of the thickening effect of the HEUR thickeners in the afore-mentioned example is assumed to be that the polyethylene glycol segments ensure the water compatibility and the hydrophobic segments construct a viscosity-imparting three-dimensional molecular association via an association with one another and also with dispersed binder particles of the emulsion paint to be thickened therein.
Thickeners are also used in the field of cosmetic preparations. Thickeners for cosmetic preparations are expected to have an adequate thickening effect even in preparations with a high content of salt. Furthermore, such thickeners should produce cosmetic preparations with a good texture and pleasant feel on the skin. Compatibility with numerous other auxiliaries, in particular with salts and surfactants, and also incorporability of the thickener itself and also of the other auxiliaries should be provided.
Moreover, the thickened preparations must have constant rheology and physical and chemical quality even upon long-term storage, and in the case of changes in temperature and pH. Finally, it should also be possible to produce these thickeners in a cost-effective manner and without a notable impact on the environment.
U.S. Pat. No. 4,079,028 and U.S. Pat. No. 4,155,892 disclose, inter alia, linear polyurethane thickeners. The preparation of the polyurethanes specified therein is catalyzed by the catalyst dibutyltin dilaurate (DBTL) customary in polyurethane chemistry.
EP 1584331 and EP 1013264 describe polyurethane thickeners for cosmetic preparations. These are prepared in a single-step process by reaction without a diluent from polyol, polyisocyanate and fatty alcohol, which may be ethoxylated if desired, and without use of a catalyst.
WO 2006/002813 describes polyurethane thickeners for various applications in aqueous media. These thickeners are prepared from hydrophilic polyols having at least two hydroxy groups, one or more hydrophobic compounds, e.g. long-chain alcohols, and at least difunctional isocyanates. Here, an excess of NCO groups is used. The catalyst used is 1,8-diazabicyclo-[5-4-0]undec-7-ene (DABCO).
WO 02/88212 describes polyurethanes of ethoxylated long-chain alcohols and cyclic diisocyanate oligomers, for example isocyanurates, as starting materials. The polyurethanes described are prepared without using a catalyst.
EP 725097 describes polyurethane thickeners, during the preparation of which polyethers, produced by alkoxylation of alcohols or alkylphenols, are reacted with polyisocyanates with catalysis by DBTL, diazabicyclooctane or tin dioctoate, the ratio of NCO to OH equivalents being in the range from 0.9:1 to 1.2:1. These thickeners are proposed for use in the field of low shear forces, e.g. for the flow of water-based emulsion paints.
EP 1241198, EP 1241199, and EP 1241200 describe the preparation of polyurethane thickeners with DBTL catalysis and use of polyetherpolyols and urethane-group-containing polyetherpolyols with functionalities >2 (for example ethoxylated sugars, glycerol, etc.).
EP 761780 and EP 1111014 describe polyurethane thickeners composed of polyethylene glycol, diisocyanate and branched, preferably long-chain-branched alkyl groups as hydrophobic component. The preparation takes place in the melt without using a catalyst.
WO 2009/135856 and WO 2009/135857 describe water-dispersible polyurethanes with an essentially linear backbone composed of alternating hydrophilic and hydrophobic sections and uses thereof. The polyurethane formation is catalyzed by titanium or zinc compounds.